New Generation in Pre-heating Technology

theMill for Minimills

CVS MAKİNA İNŞAAT SAN. ve TİC.A.Ş KR Tec GmbHDilovası Organize Sanayi Bölgesi 3. Höllstrasse 12 Kısım Muallimköy Cad. No:21 D – 77694 Kehl‐Sundheim Gebze 41400 Kocaeli / TÜRKİYE GERMANY

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Tel. +90 262 759 1505 Fax. +90 262 759 1880 Tel. +49 7851 88 67 133 Fax. Ext.134 [email protected] www.cvs.com.tr info@kr‐tec.net www.kr‐tec.net

NEW GENERATION IN PRE‐HEATING TECHNOLOGY

FOR ELECTRIC STEEL MAKING

HIGHER PRODUCTIVITY WITH REDUCED POWER

Knut RUMMLER ‐ KR Tec GmbH – Managing Director

Akif TUNABOYLU ‐ CVS TECHNOLOGY ‐ Technical Coordinator

Dogan ERTAS ‐ CVS TECHNOLOGY –Chief, Project and Contracting Department

In the steelmaking process, by scrap melting through Electric Arc Furnace route , substantial

reduction in electric power consumption and associated increase in furnace productivity can

be realized with Scrap Pre‐heating Technique which pre‐heats the scrap to about 700 °C by

making use of the sensible heat carried in the furnace off gas. In this respect, CVS

Technology has a co operation with KR Tec GmbH, which developed an ‘’environmentaly

friendly’’ and ‘’high efficiency’’ scrap preheating system to be ‘’superior’’ over the existed

systems developed so far. This challenge led to the raise of a new and superior ‘’

Environmetal Pre‐heating and Continuous Charging (EPC) System’’. The EPC System

combines the advantages of 100% scrap preheating and continuous scrap feeding through

its chambers, without the need of EAF roof opening. EPC prevents totaly, any dust emission

and heat loss during furnace charging stage, as it is the case normally for other operations.

The EPC‐EAF is a new generation, economical and environmentaly friendly Electric Arc

Furnace. Considerable reduction in electric energy consumption, increased productivity,

meeting strict environmental regulations, less dust load within the melt shop, flicker

reduction& harmonic disturbance reduction are some of the important features of the new

and superior EPC system.



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1. INTRODUCTION

Today's steelmakers are seeking for clever solutions to achive more economical, ecological

and flexible operations. These should be realized with less maintenance intensive

equipments. These are the main objectives for maintaining commercial success and

competitiveness within this sector. Continuing increase in electric energy costs, strict rules

impossed on atmospheric CO2 emissions and ever tighter environmental regulations for

land and waters lead the steelmakers to decrease their energy consumptions and to

recycle the waste materials and medias. Scrap preheating has been used for over 30 years

to offset electrical steel melting requirements. It normaly involves the use of EAF hot off

gas to heat scrap in the bucket, prior to its charging into furnace. The source of the hot gas

can be either solely the off gas from EAF and/or gas from suplementary burner(s). The

primary energy requirement for the EAF is for heating the charged scrap to its melting

point. Thus, energy can be saved, if scrap is charged to the furnace hot. Preheating of

scrap also eliminates the possibility of charging wet scrap into EAF and this eliminates the

possibility of an explosion in the furnace, in case wet scrap deeps in liquid steel . Hence,

preheating scrap also improves plant safety and accidental equipment damage. Scrap

preheating reduces EAF electrical energy consumption and increases melt shop

productivity.

Some operational parameters have shown that there is a maximum preheat temperature

beyond which further efforts to heat the scrap lead to diminished returns. This temperature

lies in the range of 540–650°C. It is estimated that by preheating the scrap to a

temperature of 425–540°C, a total of 63–72 kWh/ton of electrical energy can be saved.

Early scrap preheaters used independent heat sources. The scrap was usually heated in the

scrap bucket. Energy savings reported from this type of preheating were, as high as, 30

kWh/ton with associated reductions in electrode and refractory consumption due to

reduced tap-to-tap times.

As EAF fourth hole offgas systems were developed, attempts were made to use the EAF

offgas for scrap preheating. A side benefit reported was that the amount of baghouse dust

decreased because the dust was sticking to the scrap during preheating. Scrap preheating



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with furnace offgas is difficult to control due to the variation in offgas temperature

throughout the heat cycle. In addition, a temperature gradient forms within the scrap being

preheated. Temperatures must be controlled to prevent damage to the scrap bucket and in

order to prevent burning or sticking of fine scrap within the bucket.

Scrap temperatures can reach 315–450°C, (600–850°F), though; this will only occur at the

hot end where the offgas first enters the preheater. Savings are typically only in the

neighborhood of 18–23 kWh/ton. In addition, as operations become more efficient and tap-

to-tap times are decreased, scrap preheating operations become more and more difficult to

maintain. Eventualy, scrap handling operations actually started producing reduced

productivity and increased maintenance costs.

Some of the benefits attributed to scrap preheating are increased productivity by 10–20%,

reduced electrical consumption, removal of moisture from the scrap, and reduced electrode

and refractory consumption per unit production. Some drawbacks to scrap preheating are

that hazardous volatiles are evolved from the scrap, creating odors and necessitating a

post-combustion chamber downstream.

In addition spray quenching following post-combustion is required to prevent recombination

of dioxins and furans. Depending on the preheat temperature, buckets may have to be

refractory lined.

2. DESCRIPTION OF EPC SYSTEM

Environmental Pre-heating and Continuous Charging has many adventageous :

- MINIMUM DUST EMMISION: During charging procedure the system is always in a

closed and airtight situation which results in minimum pollution level in the meltshop

- ENERGY SAVING: The EPC reduces the electric energy consumption by approx. 100

kWh/t compared to the conventional EAF.



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- INDEPENDENT SCRAP CHARGING: Charging of the scrap basket is done with

power-on and independently from the furnace operation. This improves the

operation and reduces the power off time. Eliminating the need for EAF roof

opening substantially reduces the heat loss from furnace.

- LOW DOWNTIMES / MAINTENANCE & LESS HEAT LOSS FROM WCC: No critical

water cooled mechanical parts such as fingers, no need for conveyors and no extra

water cooled parts requirements which may cause unforeseen stoppages, need

intensive maintenance, and lead to excessive water cooling heat losses from the

furnace.

- HIGHER PRODUCTIVITY: Due to shorter power-on and power-off times. The

productivity of the furnace can be increased by 20 % compared to the conventional

EAF.

- LONGER EAF ROOF & ROOF DELTA LIVES: Due to, there is no need for

opening/closing the furnace roof for charging and electric arc is always away from

the roof, less arc damage results at roof WCP and the minimized thermal shock

additionally helps in extending roof delta life.

- HIGHER RETURN ON INVESTMENT: The EPC System features lower conversion cost

due to the preheating effect. Furthermore higher productivity because of less

power-on and power-off times are assured. Depending on the scrap quality, some

yield gain can also be expected.

- LESS FLICKER: Related to the flat bath operation, preheated scrap and the

constant energy input, a reduced flicker and harmonics level is reached. This also

leads to less arc noise generation.

- SAVINGS FOR SCRAP TREATMENT: The above saving does not take into

consideration the additional saving of approx. 10.00 EUR / t liquid, due to the fact

the EPC - System does not require any special scrap treatment.



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The new and superior EPC design considers the most flexible operational

activities.

The main features are:

- Flat bath operation.

- Controlled scrap charging rate through telescopic feeder system.

- Continuous charging during power on.

- Scrap charging rate is tuned according to melting power/preheating temperature.

- Uniform and well controlled bath temperature.

- Well controlled preheating temperature.

- Minimized off gas volume related to airtight system.



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Environmental benefits :

- Charging with closed system, into a separate compartment (EAF roof is closed,

dedusting primary line is on)

- Minimum fume emission during scrap charging

- Cleaner and safer working area

- 30% less off gas

- 30 % less dust at the filter

- Reduced arc noise level, (melting preheated scrap, melting flat bath conditions

under foamy slag)

- Direct preheating, charged scrap is exposed to very high temperatures

EPC respects to most environmental standards.

The Charging with scrap bucket is only done, for one time, and at the beginning the first

heat of an operations cycle or in case of an emergency situation.

Emission from steel making process is one of the biggest problems. Emission control

regulations are worldwide getting tighter. In the EAF field, in a sense, power saving and

scrap preheating are synonym. Various technologies have been developed to effectively

preheat the scrap by the furnace exhaust gas. One of the issues of the EPC System is to

charge the scrap independent of the electric arc furnace melting by taking into

consideration the environmental aspects. The preheating chamber of EPC is installed beside

the EAF upper shell and the preheated scrap resides in this charged continuously, by the

telescopic feeder system, into EAF for melting. This is while the furnace power is on. Even

during charging of the scrap basket into the drawer positioned in the waiting deck , the

preheating chamber is closed with the drawer’s front wall and hence the furnace and

preheating chambers are totaly isolated. This ensures little or no dust escape during

furnace charging. The scrap basket will be charged into the drawer of EPC by opening top

slide gate and while the charging drawer is positioned in the waiting deck. After charging,

top horizontal slide gate is closed and the charged scrap inside drawer is in waiting

position. Due to melting and preheating chambers are isolated during charging EPC,

melting and preheating don’t have to be interrupted. Then, the drawer is forwarded by two

hydraulic cylinders towards over the preheating chamber, horizontally, and the scrap falls



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smoothly into the preheating chamber where it gets preheated. When the drawer is over

preheating zone, its rear wall is closing the preheating chamber. A special design of the off

gas duct together with a water cooled regulation flap allows to control the preheating effect

in the preheating chamber.

The scrap basket will be charged into the drawer of EPC while it is positioned

inside waiting deck.

During charging, and when the charging drawer is positioned inside waiting deck, front wall

of the drawer closes and isolates the preheating chamber and hence the melting process in

EAF and the preheating don’t have to be interrupted.

After filling the drawer by the raised scrap basket, the slide gate on top of the EPC system

is closed.



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EPC, currently developed, is a shaft type- preheat furnace, based on AC technology. The

furnace will maintain a large hot heel ,(nearly 40 %), so that uniform operating conditions

can be maintained. Steel is tapped out periodically via a bottom taphole in the furnace.

The scrap charging system consists of two main components, the preheat chamber and the

charging deck inside which a drawer operates.

The scrap is fed into the upper part of the chamber from a receiving hopper. The exhaust

gas from the furnace flows up through the chamber, preheating the scrap. Scrap preheat

temperatures as high as 800°C can be achieved. Gas exit temperatures from the chamber

is around 200°C. At the base of the preheat chamber, there are two screw type pushers.

These operate in two stages, allowing scrap feed into the furnace at a constant rate. Offgas

leaves the top of the preheat chamber and flows to a bag filter. Some gas can be recycled

to the furnace to regulate the inlet gas temperature to the preheater.

Scrap is fed continuously to the furnace until the desired bath weight is achieved. This is

followed by a short refining and super heating period followed by tapping of the heat.

Power input is expected to be almost uniform throughout the heat. Most furnace operations

are fully automated. Charging rate of scrap into the preheater chamber is fully automated

based on the scrap height in the chamber as well as temperature of the gas. Furnace

feeding rate is interrelated to this, and to the actual power input. Carbon and oxygen

injections are controlled based on the depth of foamy slag.



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Melting cycle for 170 ton EAF (156 MVA Transformer) is given below as a sample.



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3. OPERATIONAL MODES OF EPC

1. Refining Phase of EAF

- Preheating of 1st bucket of next heat in pre-heating chamber

- Charging of next bucket into charging drawer

2. Preheating inside EPC

- Start feeding of preheated scrap after tapping

- Pre-heating chamber half empty drawer can move to waiting/charging position

3. Charging Preheating Chamber

- Moving of charging drawer into pre-heating chamber

- Preheating of 2nd bucket of next heat in pre-heating chamber

- Off gas flap closed



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4. Preheating inside EPC

- Scrap bucket in waiting position

- Continuous feeding of scrap during power on

5. Charging to Upper Hopper EPC

- Start feeding of preheated scrap

- Opening of sliding gate on top

- Charging of next bucket into charging hopper



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6. Parking Position of EPC

- EPC system is moving backward on wheel mechanism underneath

4. CONCLUSION

Without doubt, current trends in EAF design indicate that high levels of both electrical and

chemical energy are likely to be employed in future furnace designs. The degree to which

one form of energy is used over another will be dependent on the cost and availability of

the various energy forms in a particular location. There are many new processes for



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steelmaking which are now being commercialized. In almost all cases the goal is to

minimize the electrical energy input and to maximize the energy efficiency in the process.

Thus, several technologies have attempted to maximize the use of chemical energy into the

process. These processes are highly dependent on achieving pseudoequilibrium where

oxygen has completely reacted with fuel components (carbon, CO, natural gas, etc.) to give

the maximum achievable energy input to the process. Other processes have attempted to

maximize the use of the energy that is input to the furnace by recovering energy in the

offgases (Fuchs shaft furnace, Consteel, EOF, IHI Shaft). These processes are highly

dependent on good heat transfer from the offgas to the scrap. This requires that the scrap

and the offgas contact each other in an optimal way.

All of these processes have been able to demonstrate some benefits. The key is to develop

a process that will show process and environmental benefits without having a high degree

of complexity and without affecting productivity. There is no perfect solution that will meet

the needs of all steelmaking operations. Rather, steelmakers must prioritize their objectives

and then match these to the attributes of various furnace designs. It is important to

maintain focus on the following criteria:

1. To provide process flexibility.

2. To increase productivity while improving energy efficiency.

3. To improve the quality of the finished product.

4. To meet environmental requirements at a minimum cost.

With these factors in mind, the following conclusions are drawn:

1. The correct furnace selection will be one that meets the specific requirements of the

individual facility. Factors entering into the decision will likely include availability of raw

materials, availability and cost of energy sources, desired product mix, level of post furnace

treatment/refining available, capital cost and availability of a trained workforce.

2. Various forms of energy input should be balanced in order to give the operation the

maximum amount of flexibility. This will help to minimize energy costs in the long run, i.e.

the capability of running with high electrical input and low oxygen or the converse.



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3. Energy input into the furnace needs to be well distributed in order to minimize total

energy requirements. Good mixing of the bath will help to achieve this goal.

4. Oxygen injection should be distributed evenly throughout the tap-to-tap cycle in order to

minimize fluctuations in offgas temperature and composition. Thus, postcombustion

operations can be optimized and the size of the offgas system can be minimized. In

addition, fume generation will be minimized and slag/bath approach to equilibrium will be

greater.

5. Injection of solids into the bath and into the slag layer should be distributed across the

bath surface in order to maximize the efficiency of slag foaming operations. This will also

enable the slag and bath to move closer to equilibrium. This in turn will help to minimize

flux requirements and will improve the quality of the steel.

6. The melting vessel should be closed up as much as possible in order to minimize the

amount of air infiltration. This will minimize the volume of offgas exiting the furnace leading

to smaller fume system requirements.

7. Scrap preheating provides the most likely option for heat recovery from the offgas. For

processes using a high degree of chemical energy in the furnace, this becomes even more

important, as more energy is contained in the offgas for these operations. In order to

maximize recovery of chemical energy contained in the offgas, it will be necessary to

perform post-combustion. Achieving high post-combustion efficiencies throughout the heat

will be difficult. Staged post-combustion in scrap preheat operations could optimize heat

recovery further.

8. Operations which desire maximum flexibility at minimum cost will result in more hybrid

furnace designs. These designs will take into account flexibility in feed materials and will

continue to aim for high energy efficiency coupled with high productivity. For example

operations with high solids injection, iron carbide or DRI fines, may choose designs which

would increase the flat bath period in order to spread out the solids injection cycle.

Alternatively, a deeper bath may be used so that higher injection rates can be used without

risk of blow through.

9. Operating practices will continue to evolve and will not only seek to optimize energy

efficiency in the EAF but will seek to discover the overall optimum for the whole



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steelmaking facility. Universally, the most important factor is to optimize operating costs for

the entire facility and not necessarily one operation in the overall process chain. Along with

added process flexibility comes greater process complexity. This in turn will require greater

process understanding so that the process may be better controlled. Much more thought

consequently must enter into the selection of electric furnace designs and it can be

expected that many new designs will result in the years ahead. As long as there is electric

furnace steelmaking, the optimal design will always be strived for.

By the consideration of above items, CVS Technology and KR Tec companies has developed

new patented solution in Pre-heating technology.

Minimum 20 % Productıvıty Increase wıth EPC System

PRODUCTION DIFFERENCE

EPC - EAF CONVENTIONAL EAF

Transformer MVA 100 100 Tap-weight t 100 100 Net working hours h/y 7.200 7.200 Power-on Time min 32 36 Power-off time min 6 11 Tap-to-Tap-time min 38 47 Production/hour t/h 157,89 127,66

Production/year t/y 1.136.842 919.149

Difference t/y 217.693

Minimum 8 €/T Savıng In Operatıonal Cost wıth EPC System



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OPERATIONAL COST DIFFERENCE

Unit

Unit price EPC- EAF

CONVENTIONAL EAF

EUR Cons. EUR/t Cons. EUR/t

Electrical energy KWh/t

0,06 300,0 18,0

380,0 22,8

Oxygen Nm³/t

0,20 38,0 7,6

38,0 7,6

Electrodes kg/t

4,00 1,3 5,2

1,6 6,4

Fuel Nm³/t

0,20 3,0 0,6

6,0 1,2

Charged carbon kg/t

0,20 - -

7,0 1,4

Injected carbon kg/t

0,20 15,0 3,0

8,0 1,6

Scrap %

0,30 0,89 337,1

0,89 337,1

Dust removal kg/t

0,20 12,0 2,4

18,0 3,6

Lime kg/t

0,10 38,0 3,8

38,0 3,8

TOTAL

377,7

385,5 Savings EUR/t 7,8

-15

-10

-5

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5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Mill

ion

Eu

ro

Time (month)

R O I C O M PA R I S O N

EPC - EAF

CONV EAF

ROI FOR EPC-EAF

ROI FOR CONV-EAF

New Generation in Pre-heating Technology

Documents

preheating scrap

scrap bucket

scrap lead

charged scrap

scrap temperatures

scrap preheating operations

fine scrap

scrap handling operations